Method and apparatus of fabricating liquid crystal display device

ABSTRACT

A method and an apparatus of fabricating a liquid crystal display device adapted to improve a lift-off efficiency are disclosed. The liquid crystal display device is also disclosed. The method includes forming a first thin film on a substrate; forming a photo-resist pattern on the first thin film; etching the first thin film using the photo-resist pattern as a mask; forming a second thin film on the substrate having the photo-resist pattern; forming a plurality of stripper infiltration paths; and removing the photo-resist pattern and the second thin film using a stripper within the stripper infiltration paths. The device includes two substrates facing each other; a liquid crystal layer; data lines and gate lines that cross each other to define pixel regions; thin film transistors; pixel electrodes connected to the thin film transistors; and an inorganic layer in each pixel region, wherein the inorganic layer includes a plurality of cracks.

This application claims the benefit of Korean Patent Application No.10-2005-0058723, filed in Korea on Jun. 30, 2005, which is herebyincorporated by reference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a liquid crystal display device and a methodand an apparatus of fabricating the liquid crystal display device. Moreparticularly, this invention relates to a liquid crystal display devicehaving an improved lift-off efficiency and a method and an apparatus offabricating the liquid crystal display device that are adapted toimprove lift-off efficiency.

2. Description of the Related Art

Generally, a liquid crystal display device (LCD) controls the lighttransmittance of a liquid crystal having a dielectric anisotropy byusing an electric field to thereby display a picture. An LCD includes aliquid crystal display panel for displaying a picture using a liquidcrystal cell matrix and a driving circuit for driving the liquid crystaldisplay panel.

Referring to FIG. 1, a related art liquid crystal display panel includesa color filter substrate 10 and a thin film transistor substrate 20joined together with a liquid crystal 24 therebetween.

The color filter substrate 10 may include a black matrix 4, a colorfilter 6 and a common electrode 8 that are sequentially provided on anupper glass substrate 2. The black matrix 4 may be provided in a matrixon the upper glass substrate 2. The black matrix 4 divides an area ofthe upper glass substrate 2 into a plurality of cell areas that are tobe provided with the color filter 6. The black matrix 4 prevents lightinterference between adjacent cells and external light reflection. Thecolor filter 6 is provided at the cell area divided by the black matrix4 in such a manner to be divided into red (R), green (G) and blue (B)filters, thereby transmitting red light, green light and blue light. Thecommon electrode 8 may be formed from a transparent conductive layerentirely coated onto the color filter 6, and supplies a common voltageVcom that serves as a reference voltage upon driving the liquid crystal24. In order to make a surface of the color filter level with that ofthe black matrix 4, an over-coat layer (not shown) may be provided onthe color filter 6 and the black matrix 4.

The thin film transistor substrate 20 includes a thin film transistor 18and a pixel electrode 22 provided for each cell area. The cell area isdefined by a crossing between a gate line 14 and a data line 16 on alower glass substrate 12. The thin film transistor 18 applies a datasignal from the data line 16 to the pixel electrode 22 in response to agate signal from the gate line 14. The pixel electrode 22 may be formedof a transparent conductive layer and is supplied a data signal from thethin film transistor 18 to drive the liquid crystal 24.

The liquid crystal 24 having a dielectric anisotropy is rotatedaccording to an electric field generated by the data signal to controllight transmittance. Thus, a gray scale level is implemented.

Further, the liquid crystal display panel may include an alignment film(not shown) for pre-tilting an initial aligning, and a spacer (notshown) for constantly keeping a cell gap between the color filtersubstrate 10 and the thin film transistor substrate 20.

In such a liquid crystal display panel, the color filter substrate 10and the thin film transistor substrate 20 are formed by a plurality ofmask processes. Herein, one mask process includes many processes such asthin film deposition (or coating), cleaning, photolithography, etching,stripping and inspection processes, etc.

Particularly, because fabricating the thin film transistor substrateincludes a semiconductor process and requires a plurality of maskprocesses, it has a complicated fabricating process. This complicatedfabricating process acts as a major factor in the increasedmanufacturing cost of the liquid crystal display panel. Therefore, thefabricating process of the thin film transistor substrate has progressedtowards a reduction in the number of required mask processes.

For example, a method of fabricating a related art thin film transistorsubstrate may be modified to simplify the entire process by including adiffractive exposure mask in the fourth mask process. Moreover, in arecently developed process, the method of fabricating the thin filmtransistor substrate may be modified to reduce the entire process byincluding a lift-off process in the third mask process. Specifically, inthe method of fabricating the thin film transistor substrate using thethird mask process, a transparent conductive layer is initially entirelycoated onto a photo-resist pattern for forming a contact hole. Then, aphoto-resist pattern and the transparent conductive layer are removed bya lift-off process, thereby patterning the transparent conductive layer.For improving a lift-off efficiency, a stripper infiltration path may beimplemented to enable a stripper to easily infiltrate into a transparentconductive layer coated on a photo-resist pattern.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a liquid crystaldisplay device and a method and an apparatus of fabricating the liquidcrystal display device that substantially obviate one or more of theproblems due to limitations and disadvantages of the related art.

An advantage of the present invention is to provide a liquid crystaldisplay device having an improved lift-off efficiency.

Another advantage of the present invention is to provide a method and anapparatus of fabricating a liquid crystal display device that areadapted to improve a lift-off efficiency.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the method and apparatus particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a method offabricating a liquid crystal display device includes forming a firstthin film on a substrate; forming a photo-resist pattern on the firstthin film; etching the first thin film using the photo-resist pattern asa mask; forming a second thin film on the substrate having thephoto-resist pattern; forming a plurality of stripper infiltration pathsin the second thin film; and removing the photo-resist pattern and thesecond thin film using a stripper within the stripper infiltrationpaths.

In another aspect of the present invention, an apparatus of fabricatinga liquid crystal display device includes a first deposition unit to forma first thin film on a substrate; a photolithography unit to form aphoto-resist pattern on the first thin film; an etching unit to etch thefirst thin film using the photo-resist pattern as a mask; a seconddeposition unit to form a second thin film on the substrate having thephoto-resist pattern; a heat treatment unit to form a plurality ofstripper infiltration paths; and a removing unit to remove thephoto-resist pattern and the second thin film using a stripper within atleast one of the stripper infiltration paths.

In another aspect of the present invention, a liquid crystal displaydevice includes a first substrate and a second substrate facing eachother; a liquid crystal layer interposed between the first substrate andthe second substrate; data lines and gate lines on the first substratethat cross each other to define pixel regions; thin film transistors atcrossings of each of the data lines and each of the gate lines; pixelelectrodes connected to each of the thin film transistors; and aninorganic layer in each pixel region, wherein the inorganic layerincludes a plurality of cracks.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a schematic perspective view showing a structure of a relatedart liquid crystal display panel;

FIG. 2 is a sectional view showing a portion of a thin film transistorsubstrate using a lift-off process according to an exemplary embodimentof the present invention;

FIG. 3A to FIG. 3D are sectional views showing a lift-off process in amethod of fabricating a thin film transistor substrate in FIG. 2;

FIG. 4A to FIG. 4C are sectional views showing a third mask process of athin film transistor substrate according to an exemplary embodiment ofthe present invention; and

FIG. 5 is a block diagram showing third mask process units of a thinfilm transistor substrate according to an exemplary embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to an embodiment of the presentinvention, example of which is illustrated in the accompanying drawings.

Referring to FIG. 2, a thin film transistor substrate includes a pixelelectrode 118 formed on a substrate 142 and connected to a thin filmtransistor.

The thin film transistor enables a video signal applied to the data lineto be charged into a pixel electrode 118 and be stored in response to ascanning signal applied to the gate line. The thin film transistor mayinclude a gate electrode 108 connected to the gate line, a sourceelectrode 110 connected to the data line 104, a drain electrode 112positioned in opposition to the source electrode 110 to be connected tothe pixel electrode 118, an active layer 114 overlapping with the gateelectrode 108, and an ohmic contact layer 146 between the sourceelectrode 110, the drain electrode 112 and the active layer 114. A gateinsulating film 144 may be formed between the gate electrode 108 and theactive layer 114 to define a channel between the source electrode 110and the drain electrode 112.

The pixel electrode 118 may be provided at a pixel area in which aprotective or passivation film 150 and the gate insulating film 144 areremoved, and may be connected to the drain electrode 112 exposed at thepixel area.

A method of fabricating such thin film transistor substrate will bedescribed.

A gate line and the gate electrode 108 connected the gate line may beformed on a substrate 142 by a first mask process. The gate insulatingfilm 144, the active layer 114 and the ohmic contact layer 146, a dataline 104, the source electrode 110 connected the data line 104, and thedrain electrode 112 may be formed by a second mask process. Then, theprotective or passivation film 150 and the pixel electrode 118 may beformed by a third mask process.

FIG. 3A to FIG. 3D are sectional views for describing the third maskprocess for forming the protective or passivation film 150 and the pixelelectrode 118 in FIG. 2.

Referring to FIG. 3A, the protective or passivation film 150 may beformed on the gate insulating film 144 provided with the sourceelectrode 110 and the drain electrode 112. A photo-resist pattern 152may be formed on the protective or passivation film 150. A photoresistmay be patterned by a photolithography process. The photoresist isexposed, developed and patterned to form the photo-resist pattern 152.Then, the protective or passivation film 150 and the gate insulatingfilm 144 are selectively etched using the photo-resist pattern 152 as amask. The etchant may be a wet etchant, for example, a strong acid, suchas sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid,acetic acid, or any combination thereof. The wet etchant is moreselective to the protective or passivation film 150 and the gateinsulating film 144 over the photo-resist pattern 152. This may causethe protective or passivation film 150 and the gate insulating film 144to be over-etched, so that the photo-resist pattern 152 has an overhangstructure. Thus, the substrate 142 of a pixel area is thereby exposed.

Referring to FIG. 3B, a transparent conductive layer may besubstantially entirely formed on the substrate 142 with the photo-resistpattern 152, thereby providing the pixel electrode 118 at the pixel areaand providing the transparent conductive layer as a secondary layer 154.

Next, the secondary layer 154 and the photo-resist pattern 152 may beremoved by a lift-off process. A resist stripper is applied to thestructure. The stripper does not infiltrate the secondary layer 154. Thestripper accesses the photo-resist pattern 152 through an opened path151 formed by the overhang structure between the photo-resist pattern152 and the pixel electrode 118. As a result, the photo-resist pattern152 is removed in a horizontal direction by the stripper penetratinginto undersides of the photo-resist pattern, so the photo-resist patternis removed along with the secondary layer 154 as shown in FIG. 3C andFIG. 3D.

Because the opened path 151 in which the resist stripper accesses theresist is at least a few microns to hundreds of microns wide, the openedpath 151 causes the processing time of the lift-off process to beincreased.

To improve the process of fabricating a liquid crystal display accordingto the present invention, an artificial crack may be formed in thesecondary layer 154. The photo-resist pattern 152 and the secondarylayer 154 have different thermal expansion coefficients. This causes theartificial crack to be formed in the secondary layer. Accordingly, thestripper infiltrates into the secondary layer through at least oneartificial crack and the photo-resist pattern, thereby allowing thelift-off processing time to be reduced.

Exemplary embodiments of the present invention will be described withreference to FIG. 4A to FIG. 5.

FIG. 4A to FIG. 4C are sectional views showing a third mask process of athin film transistor substrate according to an exemplary embodiment ofthe present invention.

FIG. 5 shows a third mask processing device of the present invention inwhich a protective film deposition unit 160, a photolithography unit162, an etching unit 163, a transparent conductive layer deposition unit164, a heat treatment unit 166 and a lift-off unit 168 are arranged.

Referring to FIG. 4A, the protective or passivation film 150 may beformed on a substrate 142 provided with a thin film transistor by theprotective film deposition unit 160 shown in FIG. 5. The thin filmtransistor may include the gate electrode 108 connected to the gateline, the source electrode 110 connected to the data line 104, the drainelectrode 112 positioned in opposition to the source electrode 110 to beconnected to the pixel electrode 118, the active layer 114 overlappingwith the gate electrode 108, and an ohmic contact layer 146 providedbetween the source electrode 110, the drain electrode 112 and the activelayer 114. A gate insulating film 144 may be formed between the gateelectrode 108 and the active layer 114 to define a channel between thesource electrode 110 and the drain electrode 112.

Then, the photo-resist pattern 152 may be formed on the protective orpassivation film 150 by using the photolithography unit 162. Theprotective or passivation film 150 and the gate insulating film 144 maybe etched by the etching unit 163, thereby exposing the substrate 142 atthe pixel area having no photo-resist pattern 152. The gate insulatingfilm 144 may be over-etched, so that the photo-resist pattern 152 andthe gate insulating film 144 have an overhang structure, as describedabove.

The transparent conductive layer may be substantially entirely formed onthe substrate 142 left with the photo-resist pattern 152 by thetransparent conductive layer deposition unit 164. Accordingly, the pixelelectrode 118 is formed at the pixel area of the substrate 142 and thesecondary layer 154 is formed on the photo-resist pattern 152.

Referring to FIG. 4B, a plurality of stripper infiltration paths 154 a,which may be a plurality of cracks, are formed on the secondary layer154. The stripper infiltration paths 154 as are formed based on adifference of thermal expansion coefficients between the photo-resistpattern 152 and the secondary layer 154. The stripper infiltration paths154 a are formed by a heat treatment process in the heat treatment unit166. A difference of thermal expansion coefficients may exist when thesecondary layer 154 includes an inorganic layer. The inorganic layer mayinclude such materials as insulating materials, semiconductivematerials, transparent conductive materials, metals or metal alloys. Thethermal expansion coefficient of inorganic materials is in most caseslarger than the thermal expansion coefficient of organic materials.Thus, the thermal expansion coefficient of an inorganic layer, such as atransparent conductive layer, is larger than the thermal expansioncoefficient of the photo-resist pattern 152, which is an organic layer.In a photolithography process, a temperature of baking the photo-resistpattern 152 is substantially relatively low in order to provide astripper infiltration path 154 a, which may be a crack, on the secondarylayer 154 by the heat treatment process. For example, a photo-resistpattern baking temperature of the photolithography unit is approximately130° C. while the photo-resist pattern 152 is baked at approximately 80°C.-120° C. in the photolithography unit 162 of the present invention.The heat treatment unit 166 allows a thin film transistor substrateprovided with the secondary layer 154 on the photo-resist pattern 152 tobe treated by a temperature more than a baking temperature of thephoto-resist pattern 152, for example a temperature of approximately120° C.-200° C. Accordingly, at least one stripper infiltration path 154a, which may be a crack, is generated on the secondary layer 154 havinga higher thermal expansion coefficient than the photo-resist pattern152. The heat treatment unit 166 may employ a heat treatment process,such as infrared (IR) heating or using an oven, for inducing a thermalexpansion difference between the photo-resist pattern 152 and thesecondary layer 154. The heat treatment unit 166 may also employ lightenergy.

In exemplary embodiments of the present invention, at least one stripperinfiltration path may be formed by using a plasma process, a sputteringprocess, or an ion beam process. In a plasma process, charged particlesmay bombard the secondary layer 154 causing a via in the secondary layer154. In a sputtering process, particles may bombard the secondary layer154 causing a via in the secondary layer 154. In an ion beam process, afocused ion beam may be employed to strike the secondary layer 154 tocause a reaction at the surface of the secondary layer 154 and formstripper infiltration paths 154 a.

Referring to FIG. 4C, the photo-resist pattern 152 and the secondarylayer 154 are removed by a lift-off process in the lift-off unit 168.The resist stripper accesses the photo-resist pattern 152 by an openedpath 151 in which the secondary layer 154 and the pixel electrode 118are opened by the overhang structure of the photo-resist pattern 152, aswell as a stripper infiltration path 154 a formed in the secondary layer154. This allows the photo-resist pattern 152 and the secondary layer154 to be rapidly removed. Accordingly, the lift-off processing time maybe reduced and the lift-off processing capability can be improved.

The liquid crystal display device formed by using the apparatus andmethod includes a first substrate and a second substrate facing eachother, a liquid crystal layer interposed between the first substrate andthe second substrate, data lines and gate lines on the first substratethat cross each other to define pixel regions, thin film transistors atcrossings of each of the data lines and each of the gate lines, pixelelectrodes connected to each of the thin film transistors, and aninorganic layer in each pixel region, wherein the inorganic layerincludes a plurality of cracks.

In the apparatus and method of fabricating the liquid crystal displaydevice, a plurality of stripper infiltration paths is formed on thesecondary layer by a heat treatment process using a thermal expansiondifference between the photo-resist pattern and the secondary layer,thereby allowing a lift-off processing time to be reduced and a lift-offprocessing capability to be improved. Accordingly, the apparatus andmethod of fabricating the liquid crystal display device allowproductivity to be improved.

If the gate insulating film and the organic passivation film are formedbetween the pixel electrode ITO and the glass substrate, and then theheat treatment for generating the crack is practiced to the resultantstructure, a plurality of cracks may be generated in the pixel electrodeITO of the liquid crystal display device due to the difference of theheat-expansion level generated between the ITO and the organic material.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method of fabricating a liquid crystal display device, comprising:forming a first thin film on a substrate; forming a photo-resist patternon the first thin film; etching the first thin film using thephoto-resist pattern as a mask; forming a second thin film on thesubstrate having the photo-resist pattern; forming a plurality ofstripper infiltration paths in the second thin film; and removing thephoto-resist pattern and the second thin film using a stripper withinthe stripper infiltration paths, wherein forming a plurality of stripperinfiltration paths in the second thin film includes performing a heattreatment process, wherein forming the plurality of stripperinfiltration paths further includes baking the photo-resist pattern andwherein a temperature of baking is set under a temperature of the heattreatment process, wherein the temperature of baking is approximately80° C.-120° C., wherein the temperature of the heat treatment process isapproximately 120° C.-200° C., wherein the second thin film is atransparent conductive layer.
 2. The method of claim 1, wherein thephoto-resist pattern is formed of an organic material.
 3. The method ofclaim 1, wherein the first thin film is an insulating film.
 4. Themethod of claim 1, wherein the heat treatment process includes at leastone of a heating method and a light energy irradiating method.
 5. Themethod of claim 4, wherein the heating method includes an infraredheating method.
 6. The method of claim 1, wherein removing thephoto-resist pattern and the second thin film uses a lift-off process.